Viscosity grade bitumen is used to coat aggregate material for the construction and/or pavement of roads. Sulphur is mixed with bitumen to enhance properties of bitumen viz. mechanical strength, corrosion resistance, water resistance, marshal stability, fatigue, resilient modulus (MR) and the like. However, use of sulphur in bitumen for making bitumen paving mixtures is restricted due to the emission of hydrogen sulphide gas during use of sulphur extended bitumen in paving mixture preparation, its transportation or laying on the road.
H2S released while mixing sulphur with bitumen comes from several sources. The chemistry of generation of H2S is a reaction that occurs between bitumen and sulphur at temperatures greater than 120° C. Sulphur has condensing effect upon asphalt under heat resulting in the formation of gaseous hydrogen sulphide as per below given reaction:CxHy+S→CxHy-2+H2S(g)at temperature greater than 120° C., cracking of sulphur organic compounds is also responsible for liberation of H2S. H2S emission is hazardous as it directly affects the human nervous system, and therefore, it is necessary to minimize H2S emission in the aforestated process.
Occupational safety and health administration (OSHA) has established a permissible exposure limit (8 hour time-weighted average of 10 ppm and acceptable ceiling concentration of 20 ppm.)
There is, therefore, felt a need to minimize the emission of hazardous H2S gas during paving mixture preparation.